Method of cleaning steel surfaces



3,293,148 METHOD OF CLEANING STEEL SURFACES Gaillard W. Dell, Detroit, and Edwin W. Goodspeed,

Royal Oak, Mich., assignors to Hooker Chemlcal Corporation, Niagara Falls, N.Y., a corporation of New York No Drawing. Filed Feb. 27, 1964, Ser. No. 347,684

4 Claims. (Cl. 252103) This invention relates to compositions and methods for cleaning metal surfaces and more particularly relates to compositions and methods for cleaning metal surfaces after they have been subjected to a forming operation.

In the art of metal deforming, such as metal drawing, cold forming operations, and the like, a chemical coating, such as a phosphate coating, is customarily provided on the metal surface to be deformed. Before the thuscoated metal surface is subjected to the deforming operation, an additional lubricant material, such as a fatty acid soap may be applied over the phosphate coating. This combination of phosphate coating and soap lubricant has been found to provide particularly effective lubrication for the metals during the various deforming operations.

Once the deforming operation has been completed, the resulting metal article is generally subjected to an annealing or a finishing operation. Typical finishing operations include plating, the application of corrosion resistant or decorative coatings, bufiing, polishing, and the like. For the most part, the success of these subsequent finishing operations depends to a great extent on having the surface of the formed metal article substantially clean. Since appreciable quantities of the lubricant composition ordinarily remain on the metal surface following a deforming operation, a cleaning operation is generally necessary before the finishing operation can be efiected.

Ideally, such cleaning operations are carried out substantially automatically, with little or no hand operations required. However, because of the diverse nature of the materials to be removed from the metal surface, e.g., phosphate coatings and drawing lubricants, as well as oil, grease, and similar contaminants, difi'iculties have frequently been experienced in the past in obtaining a cleaning composition which is effective in removing all of these materials in a simple immersion or spray cleaning operation. Inasmuch as many of the metal deforming operations are carried out in a substantially continuous manner, it is very desirable that any cleaning operations also be effected substantially continuously over as short a period of time as possible. Heretofore, this has not always been possible and multiple cleaning operations utilizing different cleaning compositions, have sometimes been required. Accordingly, up to the present time it has not been generally possible to effect removal of materials such as phosphate coatings, drawing lubricants, oil, grease and the like in a single cleaning operation, using only one cleaning composition, at a cost which was commercially attractive.

It is, therefore, an object of the present invention to provide a novel cleaning composition which is effective in removing diverse materials such as phosphate coatings, soap lubricants, oil, grease and the like from metal surfaces.

Another object of the present invention is to provide a novel cleaning process whereby phosphate materials, soaps, oil, grease and the like are quickly and easily removed from metal surfaces.

A further object of the present invention is to provide a novel cleaning composition which has a long storage life and which is relatively simple to formulate.

United States Patent A still further object of the present invention is to provide a novel cleaning composition which may be utilized in various cleaning processes, including both immersion and spray type cleaning.

These and other objects will become apparent to those skilled in the art from the description of the invention which follows.

Pursuant to the above objects, the present invention includes a novel composition which, when dissolved in water, forms an alkaline solution, which composition comprises an alkali mwl hdroxie, an oxidizing agent, a polyethylene glyco type ionionic surface active agent, a'rid a gluconic acic mater al. As indicated hereinabove, this composition, when dissolved in water, forms an alkaline solution which is effective in cleaning metal surfaces, and is particularly effective in removing phosphate materials, soaps, oil, grease and the like, from metal surfaces such as iron, steel, zinc, alloys containing these metals and the like.

More specifically, the solid cleaner composition of the present invention may contain an oxidizing agent in an amount sufiicient to provide oxidizing ability equivalent to that of hexavalent chromium ions present in an amount from about 0.009 to about 0.6 percent by weight of the composition, a luconic acid material in an amount within the range of about i to about 37 percent by weight of the total compositiona'fia a polyethylene glycol type nonionic surface active agent inmthe range of about 0.05 to about 18 percent by weight of the total f composition, with the balance of the composition to make substantially permng substantially an alkali metal hydroxide. Generall the alkali metalmwxide will Be present in the compgsition iri a m ougtgwithig the c u QUEIEEQM b ,w ishtnt the totar'coinposition. Additionally, it will be appreciated thaf other materials which are not detrimental to the composition or the cleaning obtained may also be included in the dry, solid composition to make up to 100%. In any event, it is preferred that the amounts of substituents used in making up this solid composition should not be in excess of the solubilities of the materials in the aqueous solution, considered with respect to the amounts of the other substituents also present. The alkali metal hydroxide which makes up the major portion of the above composition is preferably sodium hydroxide. However, hydroxides of the other alkali metals, e.g., potassium, lithium, cesium and rubidium, may also be used to obtain comparable results. Moreover, it has been found that in some instances, as for example, where the cleaning composition is to be utilized in a spray cleaning operation, it may be preferable to use potassium hydroxide rather than sodium hydroxide. Inasmuch as sodium hydroxide is preferred in most instances, however, primary reference hereinafter will be made thereto. This is not, however, to be taken as a limitation on the alkali metal hydroxide which may be used in the present composition, but merely as being exemplary of such alkali metal hydroxides.

Various oxidizing agents, both organic and inorganic, have been found to be suitable for use in the present composition. Exemplary of oxidizing agents which may be used are the perman ana'tes, molybdates, perborates, peroxides, chlom iodates, perchlorates, nitrites, hypochlorites, chromates and bichromates. These materials are conveniently utilized in the form of a metallic l lprcfcrahlyau alkalimetalsalt, such sasodiumalt, although the other alkali metal salts enumerated hereinabove may also be used: Other oxidizing agents which may be used include chromic acid, picric acid, ortho- Examine nitrochloro benzene-p-sulfonic acid, m-nitrobenzoic acid and sodium meta-nitrobenzene sulfonate. Of the above oxidizing agents, sodium meta-nitrobenzene sulfonate and the strong inorganic oxidizing agents, such as those in which hexavalent chromium provides the oxidizing power are preferred. Specific examples of such preferred hexavalent chromium oxidizing agents are chromic acid, sodium chromate, sodium bichromate, and the like.

The glllcflnicaeid materials which may be used in the Fesent composition include gluconic acid itself, the alkali gluconates such as sodium gluconate, gluconodelta-lactone and the like. By the term gluconic acid materials it is intended to include materials such as those set forth specifically hereinabove as well as other materials which form gluconic acid and/or the alkali metal gluconates, in situ when placed in solution.

"y-T'hfi polyethylene glycol type nonionic surface active agents which may be used in the subject composition include various polyethylene glycols having molecular weights from about 200 to about 20,000. Of these, polyethylene glycol having a molecular weight of about 4000, e.g., Polyethylene Glycol 4000, has been found to give excellent results and is preferred. Other polyethylene glycol type materials which may also be used include Polyethylene Glycol 1000, Polyethylene Glycol 200, Polyethylene Glycol 2000, Polyethylene Glycol 20M, Polethylene Glycol 6000 and the like.

A specifically preferred composition is one containing the following substituents in the amounts indicated:

Substituent: Percent Sodium hydroxide 88-89 Sodium gluconate 8.5 Polyethylene Glycol 4000 1.6

Chromic acid or sodium chromate 0.9-1.6

For use in cleaning, the compositions as described hereinabove are desirably formulated into aqueous solutions with which the metal surfaces to be cleaned may be brought into contact. These aqueous solutions are preferably formed by dissolving the above solid compositions in water so as to form a solution containing an alkali metal hydroxide in an amount of at least 0.3 percent by weight of the total solution (3 grams per liter), a gluconic acid material in an amount of at least about 0.1 percent by weight of solution (1 gram .per liter), polyethylene glycol type of nonionic surface active agent in an amount of at least about 0.01 percent by weight of the total solution (0.1 gram per liter) and an oxidizing agent in an amount sufiicient to provide oxidizing ability equivalent to that obtained from hexavallent chromium ions present in amount of at least about 0.002 percent by weight of the total solution (.02 gram per liter). Preferably, the aqueous cleaning solution formed contains sodium hydroxide in an amount within the range of about 4 to about 20 percent by weight of the total solution, sodium gluconate in an amount within the range of about 0.4 to about 1.5 percent by weight of the total solution, Polyethylene Glycol 4000 in an amount within the range of about 0.01 to about 0.8 percent by weight of the total solution, and an oxidizing agent in an amount sutficient to provide the oxidizing ability equivalent to that obtained from hexavalent chromium ions present in an amount within the range of about 0.002 to about 0.03 percent by weight of the total composition. Where the oxidizing agent used is the preferred chromic acid, the cleaning solution preferably contains this material in an amount within the range of about 0.005 to about 0.05 percent by weight of the total solution. The aqueous alkaline cleaning solution is preferably made up in concentrations within the range of about 5 to about 230 grams of the solid composition per liter of solution, with concentrations within the range of about 55 to about 80 grams per liter being preferred. One preferred aqueous alkaline cleaning composition has a concentration of about 60 grams per liter and contains the following substituents in the amounts indicated: sodium hydroxide 53.5 grams per liter, sodium gluconate 5 grams per liter, Polyethylene Glycol 4000, 1 gram per liter and chromic acid 0.5 gram per liter.

In using the aqueous cleaning solution of the present invention, the solution is maintained at an elevated temperature above room temperature, and, where a soap or fatty acid lubricant is to be removed from the metal surface to be cleaned, preferably at a temperature above the melting point of such lubricant. Temperatures within the range of about to about 210 de recs F. are typical of those which mam within the range of about to about 210 degrees F. being preferred. It will be appreciated, however, that lower temperatures, e.g., 100 degrees F. or even lower, as well as higher temperatures, e.g., up to the boiling point of the cleaning solution may also be used in some instances with comparable results.

To efiect cleaning, the metal surface to be cleaned is contacted with the heated cleaning solution for a period of time sufficient to effect substantially complete removal of the undesirable surface materials from the metal, such as phosphate materials, soap and fatty acid lubricants, oil, grease and the like. For many cleaning operations, contact times of from about 30 seconds to about 3 minutes have been found to be typica us y, in some instances shorter contact times e.g., 10-15 seconds may also be used while longer contact times e.g., five minutes or more, may similarly be used particularly where the undesirable surface materials to be removed adhere strongly to the surface. If desired, the metal surface to be cleaned may be a g'ta-ted while in contact with the cleaning solutron, which agitation may, in many instances, materially reduce the contact time required.

Many of the methods well known in the art may be used to effect contact of the metal surface to be cleaned with the alkaline cleaning solution. For example, contact may be accomplished by immersing the metal to be cleaned in containers or tanks containing the heated alkaline cleaning solution. Alternatively, spray cleaning techniques may be used, wherein the surface of the metal article to be cleaned is contacted with a pressure spray of the alkaline cleaning solution, at an elevated temperature. As has been indicated hereinabove, for this type of cleaning procedure, the cleaning solutions of the present invention may desirably be formulated using potassium hydroxide, rather than sodium hydroxide. Additionally, if excessive foaming becomes a problem when utilizing spray cleaning techniques, various anti-foaming materials may .be added to the cleanvmh meum solvents, silicones, higher alcohols, aptifoamin' surfactants, insolubilizing salts, and the like as m in the art. These and other adjuvants may be present in amounts up to about 25% of the total dry solid composition. Another cleaning procedure which may be used with the cleaning composition of the .present invention is that utilizing a tumbling barrel.

While there are other cleaning compositions which are effective in removing some types of surface residues from metals, none has been found other than the present composition, are effective on phosphate coatinm, lubricants, oil, grease and the like, particularly in terms of the very rapid removal obtained with this composition. It is believed that the details of the above and similar processes for contacting the work pieces to be cleaned with the cleaning solution, thereby to elfect cleaning thereof, and the apparatus used in these methods, are sufiicient- 1y well known to those in the art that further description of such processes and equipment is not necessary.

In order that those skilled in the art may better understand the present invention and the manner in which it may be practiced, the following specific examples are given. In these examples, unless otherwise indicated, the temperatures are in degrees Fahrenheit and parts are by weight.

EXAMPLE 1 A cleaning composition was formulated by combining the following substances in the amounts indicated:

Parts by weight Sodium hydroxide 89 Sodium gluconate 8.5 Polyethylene Glycol 4000 1.6 Chromic acid 0.9

Grams/liter Sodium hydroxide 53.5 Sodium gluconate 5.0 Polyethylene Glycol 4000 1.0 Chromic acid 0.5

EXAMPLE 2 The aqueous alkaline cleaning solution, as prepared in Example 1, was tested for its cleaning effectiveness. The work pieces to be cleaned were cold-rolled, unpolished steel panels which had been pickled for ten minutes at 170 degrees F. in a sulfuric acid pickle and then had been given a zinc phosphate coating, followed by a neutralizing rinse and application of a lubricant film of a stearate soap. The alkaline cleaning solution of Example 1 was heated to a temperature of about 190 degrees F. and the steel panels to be cleaned were immersed in the cleaning solution for a period of about 2 minutes. Upon removing the panels from the cleaning solution they were found to be substantially free of all residue, and showed a very bright, clean metal surface.

EXAMPLE 3 The cleaning procedure of Example 2 was repeated with the exception that the test panels to be cleaned were coated with a mineral cutting oil in addition to the phosphate and soap coating. As in the previous example, after removing the panels from the cleaning solution, they were found to be of a very bright, clean metal surface, substantially free of residue.

In the following examples, aqueous cleaning solutions were formulated as in Example 1 with the exception that different materials and amounts were used, as indicated herein below.

minutes. Additionally, the metal test pieces cleaned were both steel panels and steel tubing, which test pieces had a combined weight of coating materials from about 1800 to about 2900 milligrams per square foot. In each of these instances, after removal of the metal work piece cleaned from the hot alkaline cleaning solution, the work piece was found to be substantially free of residue and had a very bright, clean metal surface.

EXAMPLE 21 A cleaning composition was formulated by combining the following in the amounts indicated:

Parts by weight Sodium hydroxide 40 Potassium hydroxide 20 Sodium meta-nitro benzene sulfonate 4 Polyethylene Glycol 4000 8 Sodium gluconate 28 From this composition, aqueous alkaline cleaning solutions were formulated by admixing the composition with water at the rate of 20, 10 and 5 pounds per 100 gallons. These solutions contained the following concentrations of the materials indicated:

These solutions were tested for cleaning effectiveness in the manner set forth in Examples 2 and 3. In each instance the metal panel removed from the cleaning solution had a very bright, clean metal surface which was substantially free from residue.

EXAMPLE 22 Two liters of an alkaline cleaning solution having the composition as described in Example 1 were formulated. This cleaning solution was heated to a temperature of 190 degrees F. and a total of 200 square feet of steel tubing, coated with the phosphate, sodium stearate soap, and oil, as described in Examples 2 and 3 was passed through the cleaning solution, the average contact time of each tube in Solution Alkali Metal Nonionic Surface Example Conoen- Hydroxide, Gluconic Acid Ma- Oxidizing Agent, g.ll. Active Agent,

tration, g./l. terial, g.ll. g./l.

56 NaOH-50.---- Na gluconate 5 Na CrO -0,25 PEG 4000-1. 56 NaOH- "do Na;CrO -0,5 PE G 4000-1. 56 NaNO -n s PEG 4000-1. 66 NaNOz-IO PEG 4000-1. 56 Na metanitro benzene PE G 40004.

sulionate-025. 66 Na metanitro benzne PEG 40004.

sulfonate-IO.

58 Naomi-2.5 PEG 4000-1. 66 NaClO3-1o PEG 4000-1. 57 Nazo -l PEG 4000-1. 66 NflzOg-lfl PE G 4000-1. 46 do Grog-0.5 PEG 4000-1. 61 Gluconic Acid-10- (Eros-0.5.. PE G 4000-1. 59 NaOH-50..-.. Gluclnic Acid-5"-.. CrO;0.5 PEG 2000-4. 57 NaOH-50 do Ci-0 0,5 PEG 6000-2. 56 .5 PE G 20M-1. 56 PE G 4000-1.

110 PE G 4000-1.

1 Polyethylene glycol.

The alkaline cleaning solutions of Examples 4 to 20 were tested for cleaning effectiveness in the manner set forth in Examples 2 and 3. In these tests, the temperature of the alkaline cleaning solution varied within the range of about 190 to about 210 degrees Fahrenheit and the immerthe solution being about two minutes. After each 10 to 20 square feet of tubing had been cleaned, the solution was replenished by adding the solid cleaner composition as described in Example 1, a total of about 187 grams of cleaner being added during the course of the cleaning of sion times used were from about 30 seconds to about 5 the 200 square feet of tubing. Upon removing the tubing from the cleaning solution, it was found to be substantially free of residue and to have a very bright, clean metal surface. Additionally, no perceptible difierence in cleanliness of the tubing was noted after cleaning of 1, 60, 130, 150 and 200 square feet of tubing.

From the above, it is seen that the alkaline cleaner of the present invention is highly effective in removing undesirable surface contaminants, such as phophate coatings, soap lubricants, oil, and the like, from metal surfaces. This composition has been shown to be effective for extended periods of use, with only periodic replenishing of the cleaner composition in the alkaline cleaning solution. Moreover, it has been found that the dry solid cleaner composition is easily formulated and has an excellent shelf life, exhibiting little or no evidences of caking even after six months or more of storage. Additionally, with regard to Examples 4 through 13, it is to be noted that the oxidizing power of the oxidizing agents used in these examples, in the amounts shown, are substantially equivalent to the oxidizing power of chromic acid in an amount Within the range of about 0.005 to about 0.05 percent by weight of the total alkaline cleaning solution, which is equivalent to the oxidizing power of the hexavalent chromium ion in an amount in the range of about 0.002 to about 0.03 percent by weight of the alkaline cleaning solution.

While there have been described various embodiments of the invention, the compositions and method described are not intended to be understood as limiting the scope of the invention as it is realized that changes therewithin are possible. It is further intended that each element recited in any of the following claims is to be understood as referring to all equivalent elements for accomplishing substantially the same results in substantially the same or equivalent manner, it being intended to cover the invention broadly in whatever form its principle may be utilized.

What is claimed is:

1. A method of cleaning steel surfaces which comprises contacting the surface to be cleaned with an aqueous alkaline solution consisting essentially of at least about 0.3 percent by weight of the solution of an alkali metal hydroxide, an oxidizing agent in an amount sufficient to provide oxidizing power equivalent to that of hexavalent chromium ions in the amount of at least about 0.002 percent by weight of the solution, at least about 0.1 percent by weight of the solution of a gluconic acid material and at least about 0.01 percent by weight of the solution of a polyethylene glycol having a molecular weight within the range of about 200 to about 20,000.

2. A method of cleaning steel surfaces which comprises contacting the surface to be cleaned with an aqueous alkaline solution consisting essentially of from about 4 to about 20 percent by weight of an alkali metal hydroxide, an oxidizing agent in an amount suflicient to provide oxidizing power equivalent to hexavalent chromium ions in an amount in the range of about 0.002 to about 0.03 percent by weight of the solution, from about 0.4 to about 1.5 percent by weight of the solution of a gluconic acid material and from about 0.01 to about 0.8 percent by weight of the solution of a polyethylene glycol having a molecular weight within the range of about 200 to about 20,000.

3. The method as claimed in claim 2 wherein the alkali metal hydroxide is sodium hydroxide, the oxidizing agent is an inorganic hexavalent chromium containing compound, and the gluconic acid material is sodium gluconate.

4. The method as claimed in claim 3 wherein the oxidizing agent is sodium bichromate.

References Cited by the Examiner UNITED STATES PATENTS 1,095,793 5/1914 Mannheim 252-156 2,314,285 3/1943 Morgan 252-156 2,615,846 10/1952 Dvorkovitz et al 252156 2,615,853 10/1952 Kirkpatrick et a1 252-331 2,861,015 11/1958 Simon 252-103 2,987,426 6/1961 Shaw 148-6.2

FOREIGN PATENTS 217,831 6/1924 Great Britain.

SAMUEL H. BLECH, Primary Examiner.

JULIUS GREENWALD, Examiner.

M. WEINBLATI, Assistant Examiner. 

1. A METHOD OF CLEANING STEEL SURFACES WHICH COMPRISES CONTACTING THE SURFACE TO BE CLEANED WITH AN AQUEOUS ALKALINE SOLUTION CONSISTING ESSENTIALLY OF AT LEAST ABOUT 0.3 PERCENT BY WEIGHT OF THE SOLUTION OF AN ALKALI METAL HYDROXIDE, AN OXIDIZING AGENT IN AN AMOUNT SUFFICIENT TO PROVIDE OXIDIZING POWER EQUIVALENT TO THAT OF HEXAVALENT CHROMIUM IONS IN THE AMOUNT OF AT LEAST ABOUT 0.002 PERCENT BY WEIGHT OF THE SOLUTION, AT LEAST ABOUT 0.1 PERCENT BY WEIGHT OF THE SOLUTION OF A GLUCONIC ACID MATERIAL AND AT LEAST ABOUT 0.01 PERCENT BY WEIGHT OF THE SOLUTION OF A POLYETHYLENE GLYCOL HAVING A MOLECULAR WEIGHT WITHIN THE RANGE OF ABOUT 200 TO ABOUT 20,000. 